This invention relates to radio and paging systems. More particularly, this invention relates to a system for reducing the air time required to convey messages via a paging system, thus increasing system capacity.
In the prior art, manufacturers have attempted to solve this capacity problem by developing two types of paging systems. The on-site, low capacity voice (sometimes called "tone and voice") systems, which utilize an identifying tone address and a voice message. Such systems typically demonstrate a call rate of 6 calls per minute with an average ten second message. The wide-area, high capacity signalling ("tone only") systems are capable of generating up to 180 calls per minute; however, no intelligence is transmitted. In a "tone only" system the person being paged only receives an alerting "beep".
More recently, manufacturers have been proposing "display" pagers as a solution to the capacity problem. "Display" pagers consist of a system for digital transmission of alphanumeric characters which are decoded and electronically displayed on the paging device via an LED type display. One problem with this approach is that in order to achieve shorter air times, the transmission data rate must be fairly high, resulting in an increased transmission bandwidth and a concomitant degradation in sensitivity. Other disadvantages of "display" type pagers include reduced battery life resulting from display usage, the high cost and lower reliability of display devices, the inconvenience of having to look at the display to obtain the message, and the complexity of the logic circuitry necessary to implement a "display" pager. Also, "display" pagers would not be compatible with existing "tone only" high capacity paging systems.